Conventional filter systems have single large area beds which are cleansed all at once. This requires storage of a quantity of clean water sufficient to backwash the entire bed. Also, there is a substantial amount of costly downtime because the filter system is of necessity out of operation during the backwashing cycle.
Another problem with such filters is that the backwashing liquid often does not permeate the entire filter bed, leaving "dead spots" where the filter media is not cleansed.
Greenleaf U.S. Pat. No. 3,312,348 shows a circular filter divided into segments to form isolated cells connected in parallel around a common central reservoir. A cell or cells can be backwashed from the reservoir while the remaining cells continue to filter influent. While Greenleaf does not require a complete system shutdown during backwashing, its complex circular arrangement cannot be readily adapted to meet the capacity requirements of a specific application without the addition or deletion of discrete circular filter systems.
Garbo U.S. Pat. No. 3,846,304 and Schreier U.S. Pat. No. 1,685,204 each show filter systems in which backwashing water and air are distributed upwardly through single large area filter beds having conically shaped bottoms. These systems do not continue to operate as filters during backwashing.
It would be desirable to have a filter system which avoids the problems of downtime and "dead spots", is compact, and does not require complex plumbing.